Mobile communications devices have become an integral part of society over the last two decades. Mobile communications devices are deployed to government personnel, and emergency service providers. In some applications, the mobile communications device is handheld, but in other applications, the mobile communications device may be more bulky, yet still portable, such as a manpack radio, as available from the Harris Corporation of Melbourne, Fla. The typical mobile communications device includes an antenna, and a transceiver coupled to the antenna. The transceiver and the antenna cooperate to transmit and receive communications signals.
Before transmission, the typical mobile communications device modulates digital data onto an analog signal. As will be readily appreciated by the skilled person, there is a plurality of modulations available for most applications.
For most communications devices, the transmitted and received signals are spectrally limited. In other words, the communications device operates within an expected frequency range, such as the ultra high frequency (UHF) range or the very high frequency (VHF) range. Because of the known operational characteristic, the communications device is usually designed to operate optimally within the expected frequency range. Nevertheless, as communications devices have become more robust in the included feature set, some applications demand operating within multiple frequency bands, i.e. multi-band devices.
In some multi-band devices, the transmit and receive architecture may comprise a plurality of paths with respective amplifiers/receivers and antennas. In other applications, there may be a common transmit and receive path with a single antenna. In these latter applications, it can be challenging to optimize the common transmit and receive path to perform optimally in each of the operational frequency bands.
In particular, it may be problematic to design optimum impedance matching for the common antenna across each operational frequency band. One approach to these design hurdles is to sacrifice optimal performance in all bands for an architecture with passable performance in the operational frequency bands. These design hurdles can be more troublesome in communications devices that are “electrically short”, i.e. where the antenna length is short relative to a resonant length at the operational frequency ranges.
U.S. Pat. No. 8,743,009 to Packer, which is assigned to the Harris Corporation, discloses an approach to an antenna system. Here, a device reduces a length of an antenna and involves an arrangement which includes an orthogonal antenna feed. The antenna includes a radiating element with a length extending along an axis. The orthogonal feed arrangement permits recovery of a portion of the spatial volume comprising the antenna, which is normally used for antenna matching circuitry. An end portion of the radiating element is chosen to be helically shaped and includes a radio frequency (RF) feed gap. The RF feed gap is coupled to a matching network, which includes elongated conductors. The matching circuitry is positioned so that the elongated conductors are adjacent to the first end portion and extend in a direction aligned with the axis, but orthogonal to the coils forming the helically shaped end portion.